There are still 10 seats left for a concert. Ticket agent A reads the number of available seats and makes a reservation of 6 seats for a customer. At the same time ticket agent B, in another office, reads the available seats and makes a reservation of 5 seats for another customer.

(a) Use this example to explain how the lost update problem may occur when transactions are processed concurrently.

(b) Use the same example to describe the two-phase locking (TPL) protocol and explain how it can be used to prevent the lost update problem.